Thin-film thermistor elements have been used as thermo sensors or infrared sensors for devices such for example as information devices, communication devices, medical devices, household appliance devices, and automobile transmission devices. The thin-film thermistor element is a sintered compact of an oxide semiconductor having a large negative temperature coefficient. In general, in such a thin-film thermistor element, electrodes are formed on a substrate, then a thermistor thin film is formed thereon, and the resultant is heat-treated at a temperature of 1400° C. or below.
Here, in a case of forming electrodes made of platinum (Pt), an alloy thereof or the like directly on an underlayer provided in the substrate, the film deposition is performed with the substrate heated at 100° C. or above, and then the electrodes made of platinum (Pt), the alloy thereof or the like are formed by patterning with gas phase etching. In this case, a film deposition apparatus needs to have a mechanism to heat a substrate. In addition, since the gas phase etching does not use a corrosive gas, a general gas phase etching apparatus performs pattern formation by using a resist as a mask. In this process, there is a problem that the insulating underlayer, the thermistor thin film and the metal such as Pt tend to easily peel off each other due to weak adherence therebetween.
Hence, in order to obtain a strong adhesive strength between the underlayer and Pt or the like, an electrode is formed in a two layer structure including an adhesive layer made of a metal, an alloy or the like for obtaining the adhesive strength, and a conductive layer made of platinum, an alloy thereof or the like (Patent Literatures 1, 2 and 3).
As conventional techniques of this kind, there have been known ones described in the following literatures (Patent Literatures: 1. JP-A No. 2000-348906, 2. JP-B Hei 3-54841, 3. JP-A No. Hei 6-61012, 4. JP-B No. 4811316, 5.JP-A No. 2008-294288).